If you think about it, those have been the two operative principles of urban planning since the the building of Ur 6,200 years ago. Cities needed to be connected to transportation links and, ideally, to be easily defended against roving armies and enemy ships. It wasn’t until Las Vegas that cities existed strictly for fun.

Today, modern megalopolises -- particularly those in the emerging world -- are being strangled by traffic jams, antiquated water and sewage systems, rolling blackouts and horrendous pollution. In Beijing, you might as well smoke, joke local residents: just walking around the city fills your lungs with the equivalent of a pack a day.

Will some object? Sure. Humanity has spent thousands of years overcoming the hazards of the natural world. Ideally, the compelling aesthetics of environmentally planned cities and homes will make people overlook that they are living within strict limits. But it will still take unprecedented planning and cooperation to make these communities a reality.